Homeowners thinking of re-insulating their homes have two ecological concerns to keep in mind when comparing “green” options: energy-efficiency in the home and their use of natural resources.

Many foam and spray-foam products are marketed as green because they’re some of the most efficient at helping homeowners control costs for heating and cooling their homes. These materials block airflow through the home, along with dusts and pollens.

But they’re not as green as salespeople would have you believe. They’re created using oil in energy-intensive processes, can leach toxins into your air, and are costly to install. Some of their benefits are also ecological weaknesses—they don’t rot in your walls, because they’re not biodegradable.

“They like to seal in your house,” said Jerry Weston, a salesperson for Bonded Logic a manufacturer of insulation based on recycled products. “We believe a house should breathe.”

Weston says that foam insulation can trap moisture in the home, leading to stale air filled with toxins and potentially mildew. His products, on the other hand, are made from natural and recycled materials like cotton or cellulose that allow more air to flow through the home.

Weston’s company has been marketing cellulose insulation for 35 years, a product made from old newspapers and treated with boric acid to be fire retardant. Cellulose insulation is loose clumps of recycled materials that can be sprayed into existing walls for retrofitting.

A newer option is cotton insulation, which comes in long rolled pads a couple inches thick. Cotton contains 85% post-industrial fibers, such as denim collected from manufacturers. Weston said that cotton provides the same energy-efficiency in the home as fiberglass, but is better at blocking noise in the home. It also resists mold, is fire retardant and LEED eligible.

Another option for homeowners who want safer-than-fiberglass insulation is to use straw bales in their walls. According to Mieke Strand of DSA Architects, straw is both a great insulator and a structural support that can replace stud framing and plywood. Straw is produced from rice husks and is a byproduct that would otherwise be thrown away. As an insulator, the straw bales are surrounded by mud clay and then stucco, and then held together by mesh wire inside the walls.